Search PubMed⌕ Search

Biomedical subjects

T W Morris

Publications and source records attributed to T W Morris.

At least 55 records · Page 3Linked to original sources
PubMed1989

A comparison of the systemic responses to rapid intravenous injections of ioxilan, iohexol, and diatrizoate in rabbits.

Rapid intravenous injections of contrast media are used for angiocardiography, intravenous digital subtraction angiography (DSA), and rapid scan computed tomography procedures. These rapid intravenous injections have been shown to produce significant hemodynamic changes that appear related to contrast media osmolality. In this study the systemic responses to 2-second injections at a dose of 1.5 mL/kg were compared for a new nonionic agent, ioxilan (350 mgI/mL), and for iohexol (350 mgI/mL), meglumine/sodium diatrizoate (370 mgI/mL), and saline. Ioxilan has a lower osmolality and viscosity than iohexol and is formulated with a 3 mM sodium citrate as a buffer and anticoagulant. All of the test solutions produced statistically significant changes in arterial pressure and respiratory rate (P less than .05, Student's t-test). The decrease in arterial pressure seen with diatrizoate (20.1%) was significantly greater than the decrease seen with either ioxilan (10.2%) or iohexol (10.2%). All of the responses observed were transient and would not be of clinical concern in a healthy patient. Ioxilan, which contains the calcium binding agent, sodium citrate, and iohexol appear to cause less systemic effects then diatrizoate.

Animals↗
PubMed1989

An in vitro study of the hemodynamic effects of catheter injections.

The injection jet from a catheter has been shown to elevate distal pressure and flow. These disturbances in flow present a problem for the application of digital arteriography to measure physiologic flow. The authors used an in vitro model to determine the primary factors responsible for the increases in distal flow with the goal that these disturbances might be estimated and minimized. Experiments were performed to evaluate the importance of the cross-sectional area of the catheter and vessel, the importance of absolute vessel flow, and the importance of distal resistance. A lumped resistance model predicted the flow changes to within 3% of the preinjection vessel flow. In the model system the elevation of distal flow in percent was equal to (the injection rate divided by the tube flow rate) multiplied by (the proximal resistance divided by the total resistance) multiplied by 100. Because the resistance ratio generally is small, injections at physiologic flow rates should produce acceptably small increases in distal flow. The use of a large diameter catheter or the presence of a proximal stenotic lesion would increase the ratio.

Catheterization, Peripheral↗
PubMed1988

Role of angiotensin II in renal hemodynamic functions during the initial stages of acute ureteral obstruction.

This investigation examines the role of Angiotensin II in renal hemodynamic functions during acute unilateral ureteral obstruction (UUO) in a dog model. An electro magnetic flow probe was utilized to assess renal blood flow while the arteriovenous extraction technique of technetium 99m DTPA was utilized for the assessment of changes in filtration fraction and glomerular filtration rate. The effects of Angiotensin II receptor blockade on renal hemodynamic functions during acute UUO was evaluated in six dogs and compared to acute ureteral obstruction without receptor blockade in seven dogs. Angiotensin II blockade with (Sar1, Thr8)-Angiotensin II during UUO led to a striking increase in renal blood flow that was significantly different in comparison to normalized values from UUO alone (+delta 63 +/- 17 vs. +delta 22 +/- 6% at 30 min; p less than 0.05). There were, however, no significant differences in the magnitude of the decrease in filtration fraction and glomerular filtration rate in comparison to UUO alone. This investigation demonstrates that Angiotensin II has an inhibitory effect on the initial increase in renal blood flow with acute UUO. The possibility of successful pharmacologic intervention in the setting of UUO can be examined using animal models similar to the one described here. Pharmacologic treatment in the setting of acute UUO in patients might permit better preservation of renal function.

Angiotensin II↗
PubMed1988

Ventricular fibrillation during right coronary arteriography with ioxaglate, iohexol and iopamidol in dogs.

Radiograph contrast media (CM) are known to produce myocardial disturbances during cardiac angiography. The most severe electrical disturbance is ventricular fibrillation (VF). Previous studies using prolonged right coronary exposures have demonstrated a higher incidence of VF with dilute low sodium CM than with dilute CM containing more physiologic levels of sodium. In this study the incidence of VF was examined for more conventional concentrations of iopamidol, iohexol and ioxaglate and for sodium supplemented iohexol. The incidence of VF was determined during 25-second injections of contrast media into the canine right coronary artery at a rate of 0.4 mL/sec. Injections of iohexol and iopamidol at concentrations of 160, 240 and 320 mgI/mL produced significantly more VF (P less than .005, Fisher Exact Test) than meglumine/sodium ioxaglate or iohexol supplemented with 20 mM sodium chloride. The time required to produce a 50% incidence of VF with iohexol and iopamidol was significantly related to sodium concentration (r = .92, P less than .01).

Animals↗
PubMed1988

The cardiovascular effects of iodinated contrast media injections.

Intravascular iodinated contrast media are used in high doses and high concentrations to achieve the necessary x-ray attenuation. These solutions have densities, viscosities, and osmolalities considerably higher than body fluids. The properties of the solutions are responsible for many of the dose-dependent side effects of intravascular injection. There are significant differences among the media available today; however, all will produce some side effects.

Cardiovascular System↗
PubMed1988

The importance of sodium concentration on the incidence of fibrillation during coronary arteriography in dogs.

Coronary arteriography is known to produce electrical disturbances including conduction disturbances, arrhythmias, and ventricular fibrillation. A canine model for studying ventricular fibrillation has been developed that uses relatively long injections in the right coronary artery. In experiments in 49 dogs over a five-year period, the authors have consistently observed that with low osmolality contrast media, the incidence of ventricular fibrillation becomes quite high when the formulation contains less than 3.2 mmol/L sodium. This effect seems independent of the concentration of the contrast media molecules. High concentrations of the ionic monomer diatrizoate cause fibrillation despite high sodium concentrations.

Angiography↗
PubMed1988

In vitro models for testing the metabolic effects of myelographic contrast media.

Water-soluble nonionic x-ray contrast media have greatly improved the quality and safety of myelography. Toxic side effects are still observed however. The side effects are generally worse with the first nonionic agent, metrizamide, which has a glucoselike side group. Two in vitro models were developed to examine the effects of contrast media on glucose metabolism. Using rat hippocampus slices, the authors observed significant depression of carbon dioxide production by metrizamide and by deoxyglucose, a known metabolic inhibitor. Iohexol and iopamidol did not cause significant depressions. In rat brain synaptosomes the authors did not observe a depression of the uptake of deoxyglucose 14C by any media tested. These studies indicate that metrizamide can create metabolic depression but that it does not compete with glucose for the membrane glucose carrier.

Animals↗
PubMed1988

Effects of the magnetic resonance contrast medium ferrioxamine methanesulfonate on systemic and renal hemodynamics in the anesthetized dog.

Ferrioxamine methanesulfonate (S-FDF) is a new magnetic resonance (MR) contrast agent developed to improve magnetic resonance imaging of the abdomen and pelvis. This stable complex of deferoxamine methanesulfonate and iron is excreted in the urine by glomerular filtration modified by active renal tubular resorption. This study examines the acute systemic and renal hemodynamic responses to this agent after intravenous administration either as an infusion of 25 mg/kg over 5 minutes or as a rapid bolus at a dose of 50 mg/kg. In eight anesthetized dogs, renal plasma flow (RPF) was measured with an electromagnetic flowmeter, and GFR was determined by the renal extraction of technetium-99m-DTPA. Mean arterial pressure (MAP), pulse rate, and a lead II ECG were assessed. At a dose of 25 mg/kg over 5 minutes, MAP decreased significantly (control 146.0 +/- 6.5 mm Hg vs. 107 +/- 18 mm Hg at 2 minutes; P less than .05). In two of the eight animals, the MAP dropped below 60 mm Hg. Significant decreases in GFR and RPF also were noted. All four of the animals receiving the rapid injection of S-FDF experienced profound hypotension (MAP less than 50 mm Hg). The drop in heart rate from 152 +/- 11.6 bpm to 121 +/- 4.9 bpm was associated with a marked depression of the ST wave in the lead II ECG. Further animal studies are needed to assess the mechanism of toxicity and a potential synergism of action with pentobarbital anesthesia.

Animals↗
PubMed1987

Separation of internal derangements of the temporomandibular joint using sound analysis.

This clinical-arthrographic investigation compares power spectral analysis of temporomandibular joint sounds with different arthrographic characteristics of intracapsular dysfunction. The quantitative comparison of specific parameters of the sound power-spectrum waveform may provide a sensitive and accurate noninvasive tool for diagnosis and treatment.

Arthrography↗
PubMed1987

Further support for the glucose hypothesis of metrizamide toxicity. The effect of metrizamide and glucose analogue-free contrast media on hexokinase.

Metrizamide neurotoxicity has been hypothesized to be caused by an inhibitory effect of the drug on glucose metabolism. Metrizamide contains a glucose side chain, and glucose analogues including metrizamide have been shown to be inhibitors of hexokinase, an enzyme that is central to cerebral glucose metabolism. We studied the effect of the nonionic contrast agents iohexol, iotrol, and iopamidol, and the ionic contrast meglumine diatrizoate, on hexokinase in vitro. Although metrizamide reproducibly caused competitive inhibition of the reaction, the nonglucose contrast agents had no significant effect on the enzyme. These results add further support for the glucose hypothesis of metrizamide neurotoxicity.

Contrast Media↗
PubMed1987

Effect of multiple intravenous injections of diatrizoate on iodine concentrations and osmolality. An experimental study in rabbits.

Multiple intravenous injections of contrast media are used in radiology, but information regarding corresponding changes in the serum iodine concentrations and osmolality is lacking. We measured the changes in serum iodine concentration and serum osmolality in rabbits after a series of intravenous injections of contrast media. Hypaque-76 (1 cc/kg) was injected intravenously in awake rabbits at 10-minute intervals for 1 hour and arterial blood sampled at midpoint times between injections. During the 1-hour period of seven serial injections, mean serum iodine concentration at 5 minutes was 2.3 mg I/cc (+/- 0.1 SEM, n = 14); at 35 minutes, 5.1 mg I/cc (+/- 0.2); and at 65 minutes, 6.7 mg I/cc (+/- 0.4). The mean peak concentration was 6.8 mg I/cc (+/- 0.4). Serum osmolality underwent a mean increase of 16 mosm/kg during the injection period. Hypertonic mannitol injections produced a smaller increase in osmolality (10 mosm/kg). Isotonic saline injections in control animals produced no change in osmolality.

Animals↗
PubMed1987

Physiologic changes during high field strength MR imaging.

High field strength MR imaging systems may require several kilowatts of RF power to obtain images. A fraction of this power is absorbed by the patient, and changes in body temperature have been measured in experimental animals. The purpose of this study was to quantify changes in body surface temperature and other physiologic parameters in humans during MR scanning at 1.5 T. Blood pressure, heart rate, respiration, and axillary temperature measurements were obtained on 27 normal volunteers. Measurements were made at RF power levels of 0, 0.2, and 0.8 W/kg, with the power sequence randomized. In 14 volunteers receiving lumbar scans, statistically significant increases in temperature were observed at RF power levels of 0.2 (+0.2 +/- 0.1 degree C) and 0.8 (+0.5 +/- 0.1 degree C) W/kg. No significant changes related to RF power were observed in blood pressure or respiratory rate. At the 0.8 W/kg level there was a slight increase in heart rate (3 +/- 1.3 beats per minute). In the 13 patients receiving head scans, physiologic changes were substantially smaller. The temperature increases and other physiologic changes observed during MR scanning with the 1.5 T imager at RF powers of 0.2 and 0.8 W/kg were small and of no clinical concern. Additional studies should be performed in patients with cardiac failure, vascular occulusion, and metallic implants or prostheses.

Adult↗
PubMed1987

Properties and pharmacology of intravascular radiocontrast media.

The new low osmolality contrast media iohexol, iopamidol and ioxaglate produce far smaller alterations in physiologic function and far less pain than do ionic monomer agents of the same iodine concentration. It appears from the clinical information currently available that they are likely to produce fewer serious side effects. The new agents are, however, still not perfect. They still must be used with care and attempts must be made to minimize injected doses and concentrations. In this observer's opinion a real danger exists that the substantial benefits of the new low osmolality agents will be misinterpreted as complete safety.

Angiocardiography↗
PubMed1986

Effects of contrast media on renal function and subcellular morphology in the dog.

The effects of intravenous contrast media (CM) on renal excretory function and subcellular morphology are examined in this animal investigation. A decrease in GFR (12.0 +/- 1.6 vs. control 30.2 +/- 2.5 ml/min) was observed when renal function was evaluated by means of the artero-venous extraction method with Tc99m DTPA and the anticipated inverse relationship to urinary flow (Vml/min) noted. An artifactual increase in GFR (43.5 +/- 10.0 vs. control 39.1 +/- 3.8 ml/min) was observed using the timed urinary clearance of inulin. V(ml/min) increased four-fold (0.6 +/- 0.16 control vs. 2.7 +/- 0.7 ml/min; P less than .05) over the first five minutes after injection of CM. Urine osmolality initially approached isotonicity and then returned toward preinjection values. Osmolal clearance (Cosm) rose 2.5 times (1.4 +/- 0.3 control vs. 3.7 +/- 1.0 ml/min; P less than .05). The fractional excretion of both Na+ (FENa+) and K+ (FEK+) increased. A comparison of urinary osmolality vs. time after injection of CM confirms a nonspecific osmotic effect on tubular (and hence total urine) flow. The hemodynamic effects of CM on the kidney via the i.v. route reflect a predominant and nonspecific osmotically mediated vasodilation. No significant light or electron microscopic changes were observed. These findings suggest that the major renal physiologic actions of hypertonic CM are a nonspecific response to agent osmolality.

Animals↗
PubMed1986

Penetration of subarachnoid contrast medium into rabbit spinal cord. Comparison between metrizamide and iohexol.

The penetration into rabbit spinal cord of two nonionic contrast media, iohexol and metrizamide, and a reference tracer, technetium DTPA, were compared. The spinal subarachnoid space was perfused for 4 hours with a CSF solution to which technetium DTPA and either iohexol or metrizamide had been added. The contrast media and technetium DTPA concentrations reached a plateau level in CSF outflow within 80 minutes. The contrast media concentrations in CSF were higher than the technetium DTPA (P less than .001). In the cord tissue, technetium DTPA reached higher concentrations than the contrast media (P less than .001), and iohexol reached higher concentrations relative to technetium DTPA than metrizamide (P less than .001). The mean contrast media distribution volumes in the thoracic cord were 13% (iohexol) and 12% (metrizamide). The smaller distribution volume observed for metrizamide could be related to the larger effective size of "associated" metrizamide molecules or an interference with diffusion perhaps related to binding to glucose carriers.

Animals↗